I just saw this post for first time, and since I have awful vision. I have dictated text and emails to Siri on iphone and ipad when I first got them years ago. After I finish them, I take out my magnifying glass to look for errors and edit them before ever sending. These things do a good job, but maybe I could enunciate better and there would be fewer errors.
Bottom line, although this can be a faster way to get the message created, too many errors occur and there is no way I will send an important message this way to anyone unless I see the results before hitting Send unless my message was a one or two word comment. I would never use the feature on Alexa, as I have had a lot of voice composing of text with dodgy results.